Logic analyzers are digital data acquisition instruments that allow a user to acquire and analyze digital data from a large number of logic signals, such as all of the address, data and control signals associated with a microprocessor. Each logic signal is compared to a logic threshold or thresholds and results into one of two logic states, high or low, 1 or 0, true or false. The behavior of groups of these signals can then be monitored to analyze the behavior of the circuitry or instrument under test.
The time at which the state of the logic signals under analysis is resolved into binary form is determined by a clock signal. If this clock signal is generated by the logic analyzer and is independent of the system under test, the acquisition is said to be “asynchronous.” If the clock signal is derived from the system under test so as to bear a predetermined timing relationship to part of the activity within that system, the acquisition is said to be “synchronous.”
U.S. Pat. No. 5,526,286, issued Jun. 11, 1996, to Sauerwein et al. for “Oversampled Logic Analyzer” discloses a digital oversampling system and is incorporated herein by reference in its entirety. In the disclosed oversampled logic analyzer, all data and clock signal inputs are acquired asynchronously at high speed using a digital fast-in slow-out (FISO) acquisition circuit which produces a plurality of parallel high-speed data samples within each cycle of an internal system clock. The sample interval utilized is greater than the set up and hold time of the sampling device. Thus, the resulting samples are monotonic and statistically independent. In the disclosed oversampling system data and clock signals are sampled, thereby incurring sampling errors of ±1 sample interval. For example, in the case of a 125 picosecond sample interval (8 GHz oversampling), the theoretical best case setup and hold specification for such a system is two sample intervals or 250 picoseconds. However, this setup and hold specification is further degraded by sample position errors, calibration errors, random noise and other noise sources such that a useful measured value is produced at, approximately, a 500 picosecond sample interval range.